linux-kernel - Re: PS3: trouble with SPARSEMEM

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Date:	Thu, 6 Dec 2007 10:55:07 +0100 (CET)
From:	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
To:	Yasunori Goto <y-goto@...fujitsu.com>
cc:	Geoff Levand <geoffrey.levand@...sony.com>,
	Andrew Morton <akpm@...ux-foundation.org>, miltonm@....com,
	clameter@....com, apw@...dowen.org, linux-kernel@...r.kernel.org
Subject: Re: PS3: trouble with SPARSEMEM_VMEMMAP and kexec

On Thu, 6 Dec 2007, Yasunori Goto wrote:
> > I'll try Milton's suggestion to pre-allocate the memory early.  It seems
> > that should work as long as nothing else before the hot-plug mem is added
> > needs a large chunk.
> 
> Hello. Geoff-san. Sorry for late response.
> 
> Could you tell me the value of the following page_size calculation
> in vmemmap_populate()? I think this page_size may be too big value. 
> 
> ------
> int __meminit vmemmap_populate(struct page *start_page,
>                                        unsigned long nr_pages, int node)
>                            :
>                            :
>         unsigned long page_size = 1 << mmu_psize_defs[mmu_linear_psize].shift;
>                            :
> -------

24 MiB

> In addition, I remember that current add_memory() is designed for
> only 1 section's addition. (See: memory_probe_store() and
> sparse_mem_map_populate().
> they require only for 1 section's mem_map by specifing
> PAGES_PER_SECTION.)
> The 1 section size for normal powerpc box is only 16MB.
> (IA64 -> 1GB, x86-64 -> 128MB).
> 
> But, if my understanding is correct, PS3's add_memory() requires all
> of total memory. I'm afraid something other problems might be hidden
> in this issue yet.
> 
> (However, I think Milton-san's suggestion is very desirable. 
>  If preallocation of hotadd works on ia64 too, I'm very glad.)

PS3 initially starts with 128 MiB.
Later hotplug is used to add the remaining memory (96 or 112 MIB, IIRC).

With kind regards,
 
Geert Uytterhoeven
Software Architect

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